Onagraceae

Herbs, annual or perennial, shrubs, or subshrubs, [lianas or trees], terrestrial, amphibious, or aquatic, unarmed, not clonal; often with epidermal oil cells, usually with internal phloem, abundant raphides in vegetative cells. Stems erect to decumbent or prostrate. Leaves usually deciduous, usually alternate or opposite, sometimes whorled, simple, usually cauline, sometimes basal and forming rosettes; stipules present, intrapetiolar, usually caducous, relatively small, or absent (tribes Epilobieae and Onagreae); sessile or subsessile to petiolate; blade margins usually entire, toothed, or pinnately lobed, rarely bipinnately lobed. Inflorescences axillary, flowers solitary, leafy spikes, racemes, or panicles. Flowers usually bisexual, (protandrous in Chamaenerion, Clarkia, Epilobium, [and most species of Lopezia]; protogynous in Circaea and Fuchsia), sometimes unisexual (gynodioecious or dioecious, [subdioecious]), usually actino­morphic, sometimes zygomorphic, (2–)4(–7)-merous; perianth and androecium epigynous; sepals persistent after anthesis (in Ludwigia), or all flower parts deciduous after anthesis; floral tube present or absent in Chamaenerion, Ludwigia, [and most species of Lopezia]; sepals usually green or red, rarely pink or purple, valvate; petals present, rarely absent, often fading darker with age, imbricate or convolute, sometimes clawed; nectary present; stamens 2 times as many as sepals and in 2 series, antisepalous set usually longer, rarely all equal (Chamaenerion), or as many as sepals, [in Lopezia reduced to 2 or 1 plus 1 sterile staminode]; filaments distinct; an­thers usually versatile, sometimes basifixed, dithecal, polysporangiate, with tapetal septa, sometimes also with parenchymatous septa, opening by longitudinal slits, pollen grains united by viscin threads, (2 or)3(–5)-aperturate, shed singly or in tetrads or polyads; ovary inferior, usually with as many carpels and locules as sepals, rarely 1 or 2 (Circaea and Gayophytum), septa sometimes thin or absent at maturity; placentation axile or parietal; style 1, stigma 1, with as many lobes as sepals or clavate to globose, papillate or not, and wet with free-running secretions to dry without the secretions; ovules 1 to numerous per locule, in 1 or several rows or clustered, anatropous, bitegmic. Fruit a loculicidal capsule or indehiscent berry or nutlike. Seeds smooth or sculptured, sometimes with a coma or wings, with straight, oily embryo, 4-nucleate embryo sac, endosperm absent. x = 7, 8, 10, 11, 15, 18.

Distribution

North America, Mexico, West Indies, Bermuda, Central America, South America, Eurasia, Africa, Atlantic Islands, Indian Ocean Islands, Pacific Islands, Australasia, nearly worldwide, primarily New World.

Discussion

Genera 22, species 664 (17 genera, 277 species in the flora).

Members of the Onagraceae are especially richly represented in North America. The family comprises annual and perennial herbs, with some shrubs and a few small to medium-sized trees. Most species occur in open habitats, ranging from dry to wet, with a few species of Ludwigia aquatic, from the tropics to the deserts of western North America, temperate forests, and arctic tundra; some species of Epilobium, Ludwigia, and Oenothera can be weeds in disturbed habitats. Members of the family are characterized by 4-merous flowers (sometimes 2-, 5-, or 7-merous), an inferior ovary, a floral tube in most species, stamens usually two times as many as sepals, and pollen connected by viscin threads. Flowers are usually bisexual, sometimes unisexual, and plants are gynodioecious, matinal, diurnal, or vespertine, self-compatible or self-incompatible, often outcrossing and then pollinated by a wide variety of insects or birds, or autogamous (P. H. Raven 1979; W. L. Wagner et al. 2007).

Onagraceae are known in considerable systematic detail, and information is available on comparative breeding systems and pollination biology, on chromosome numbers and cytogenetic relations, often involving translocations, and on vegetative, floral, and seed anatomy, palynology, and embryology. The phylogeny of the family is known in reasonably good detail, with most parts of the trees generally well-supported.

The suprageneric and generic classification presented by W. L. Wagner et al. (2007) differs in a number of ways from the previous classification (P. H. Raven 1979, 1988). Onagraceae are divided into two subfamilies based on a fundamental basal split recognized in all phylogenetic studies (R. H. Eyde 1981; P. C. Hoch et al. 1993; R. A. Levin et al. 2003, 2004; V. S. Ford and L. D. Gottlieb 2007), with Ludwigia on one branch (as Ludwigioideae), and the rest of the family on a second branch (as Onagroideae). Onagroideae are subdivided into six tribes: Circaeeae (including Fuchsieae), Epilobieae, Gongylocarpeae, Hauyeae, Lopezieae, and Onagreae. The Epilobieae and Onagreae are diverse; together they constitute fully two-thirds of the species in the family and include 15 of the 22 genera. The classification following Wagner et al. can be viewed on the Onagraceae web site by Wagner and Hoch at http://botany.si.edu/Onagraceae.

Selected References

None.

Lower Taxa

Onagraceae subfam. Ludwigioideae, Onagraceae subfam. Onagroideae

Illustrations

Onagraceae Illustrations

Key

1	Sepals persistent or tardily caducous after anthesis; flowers (3 or)4 or 5(–7)-merous; floral tube absent; petals yellow or white [Onagraceae subfam. Ludwigioideae].	Ludwigia
1	Sepals deciduous after anthesis (along with other flower parts); flowers (2–)4-merous; floral tube usually present, often elongate, if absent then petals usually rose purple or pink, rarely white [ Onagraceae subfam. Onagroideae].	> 2
2	Stipules present and soon deciduous; fruit indehiscent (berry or burlike capsule with hooked hairs) [Onagraceae subfam Onagroideae tribe Circaeeae].	> 3
2	Stipules absent; fruit usually a capsule, sometimes indehiscent.	> 4
3	Fruit a berry; seeds few to ca. 500; flowers 4-merous.	Fuchsia
3	Fruit a capsule, burlike, with stiff, hooked hairs; seeds 1 or 2; flowers 2-merous.	Circaea
4	Seeds usually comose, coma rarely secondarily lost; sepals erect or spreading; stigmas with dry multicellular papillae, entire or 4-lobed, lobes commissural; x = 18 [Onagraceae subfam Onagroideae tribe Epilobieae].	> 5
4	Seeds not comose; sepals reflexed; stigmas usually wet, non-papillate, and entire or (3 or)4-lobed (non-commissural), sometimes (Clarkia) lobes commissural and then with dry unicellular papillae; x = 7 [Onagraceae subfam Onagroideae tribe Onagreae].	> 6
5	Floral tube absent; stamens subequal; style deflexed at anthesis, later erect, stamens initially erect, later deflexed; leaves usually alternate, rarely subopposite or subverticillate proximally.	Chamaenerion
5	Floral tube present; stamens in 2 unequal whorls; style and stamens erect; leaves opposite, at least near base of stem.	Epilobium
6	Stigmas with commissural lobes and dry, unicellular papillae; flowers usually protandrous.	> Clarkia
6	Stigmas hemispherical to subglobose or subcapitate, peltate, or 4-lobed, not commissural, surface wet, non-papillate; flowers not protandrous.	> 7
7	Ovaries 2-locular; stems usually delicate.	Gayophytum
7	Ovaries (3 or)4-locular; stems usually not especially delicate.	> 8
8	Seeds with concave and convex sides, concave side with a thick wing, convex side covered with glasslike, clavate hairs; petals white with yellow basal area.	Chylismiella
8	Seeds not concave/convex and not with a wing and clavate hairs; petals yellow, purple, red, or white, if white, mostly without yellow base.	> 9
9	Ovaries with a slender, sterile apical projection; plants usually acaulescent.	> 10
9	Ovaries without an apical projection; plants usually caulescent, sometimes acaulescent (in Oenothera).	> 11
10	Herbs perennial; sterile projection of ovary persistent with fertile part in fruit, projection without visible abscission lines at its junctures with floral tube or fertile part of ovary.	Taraxia
10	Herbs annual; sterile projection of ovary with visible abscission lines at its junctures with both short floral tube and fertile part of ovary.	Tetrapteron
11	Styles with peltate indusium at base of stigma, at least at younger stages prior to anthesis; stigmas (3 or)4-lobed, receptive all around (or peltate to discoid or nearly square in sect. Calylophus).	Oenothera
11	Styles without indusium; stigmas usually subglobose to globose, subcapitate, capitate, or cylindrical (Eulobus), rarely conical-peltate and ± 4-lobed.	> 12
12	Seeds in 2 rows per locule; capsules pedicellate; leaves mostly basal, blades often pinnately lobed, rarely bipinnately, sometimes unlobed, or lateral lobes greatly reduced or absent, terminal lobe usually large, abaxial surface of leaves or leaf margins with conspicuous, usually brown, oil cells.	Chylismia
12	Seeds in 1 row per locule; capsules usually sessile, rarely very shortly pedicellate; leaves not predominately basal, blades not lobed or pinnatifid, leaves without oil cells.	> 13
13	Petals usually white, rarely red or tinged red; flowers vespertine.	Eremothera
13	Petals yellow, often with red flecks or spots; flowers diurnal.	> 14
14	Flowering stems virgate; leaf blades pinnatifid to lobed; petals yellow with red flecks near base; seeds usually with purple spots; floral tube with a lobed disc.	Eulobus
14	Flowering stems not virgate; leaf blades not pinnatifid, margins entire or toothed; petals yellow, sometimes with 1+ red spots at base; seeds without purple spots; floral tube without a lobed disc.	> 15
15	Stems densely leafy distally, nearly leafless proximally, with many slender, ascending branches from base; capsules strongly flattened, straight.	Neoholmgrenia
15	Stems usually leafy throughout, branched throughout or with a few basal branches; capsules not flattened, subterete or 4-angled, often flexuous or curled, sometimes straight.	> 16
16	Capsules subterete; flowers only from distal nodes; seeds appearing smooth, glossy, triangular in cross section.	Camissonia
16	Capsules 4-angled, at least when dry; flowers from basalmost to distal nodes; seeds dull, flattened.	Camissoniopsis